The present invention relates to a saturable reactor to be employed in a television set and a cathode-ray tube display, particularly a saturable reactor suited to be built in a deflection yoke for the in-line type cathode-ray tube having the self convergence system.
Lately, an in-line type cathode-ray tube in which electron beams are emitted in a horizontal arrangement is widely used. In this cathode-ray tube, three electron beams can be converged within the specified tolerance over the full range of the screen only with the deflection yoke by generating the horizontal deflection field of the deflection yoke at a pin-cushion type field and the vertical deflection field as a barrel type field.
In other words, in case of a cathode-ray tube with a small deflection angle of approximately 70.degree., both primary and secondary convergence errors can be within the tolerances.
However, if the deflection angle is large, for example, 100.degree. or 110.degree., the difference between the distance from the center of deflection to the imaginary spherical surface and the distance from the center of deflection to the screen increases and the raster on the screen is affected not only by the primary and secondary convergence errors but by a higher order convergence error. It is difficult to make a deflection deflection yoke in which these convergence errors are simultaneously controlled to be within the tolerance only by the deflection coils.
For example, if a deflection yoke which generates a deflection yoke with generates a deflection field as described above is employed in a cathode-ray tube with a large deflection angle, a cross misconvergence as shown in FIG. 1 is generated. When the horizontal direction of the screen is assumed as the X axis and the vertical direction as the Y axis, an S-ing misconvergence occurs at upper and lower end parts Y.sub.T and Y.sub.B of the screen in the Y-axis direction and a positive cross (plus trapezoidal) misconvergence occurs at the four-divided positions of the screen in the Y-axis direction or the middle parts Y.sub.TM and Y.sub.BM in the Y-axis direction despite the rasters of blue beam B and red beam R positioned at right and left sides of the axis of the cathode-ray tube are converged at every point on the X and Y axes.
These different types of misconvergences which appear simultaneously on the screen cannot be eliminated by a simple means such as addition of a magnetic member and, if a convergence device is employed, the misconvergence remains on a part of the screen and the picture quality cannot therefore be improved.
The above-mentioned S-ing misconvergence can be changed to a positive cross misconvergence as shown in FIG. 2 by varying the distribution or shape of conductor winding of the saddle horizontal deflection coil or applying a single or plural sheets of magnetic members to the surface of the coil. However, the magnitude of the misconvergence at the middle part S1 and the end part PQ.sub.V in the X-axis direction which are at the upper and lower end parts Y.sub.T and Y.sub.B of the screen is not proportional to that of the misconvergence at the middle part S2 and the end part S3 in the X-axis direction which are on the middle parts Y.sub.TM and Y.sub.BM of the screen, and, even if the convergence device is employed, the misconvergence remains in the rasters and such high quality picture as demanded for displaying characters cannot be obtained.